ransburg



June 8, 1948. P, RANSBURG 2,442,986

' ELECTROSTATIC comma METHOD AND- APPARATUS Filed Jan. 26, 1945 2 Sheetsrheet 1 IN V EN TOR.

June 8, 1948. H. P. RANSBURG ELECTROSTATIC COATING METHOD AND APPARATUS 2 Sheets-Sheet 2 Filed Jan. 26, 1945 6 5 mm M V r e MUM Patented June 8, 1948 ELECTROSTATIC COATING APPARATU METHOD AND s Harold P. Ransburg, Indianapolis, Ind., assignor,

by mesne a ssignments, to Ransburg Electro- Coating Corp., Indianapolis, Ind., a corporation of Indiana Application January 26, 1945, Serial No. 574,721

1 9 Claims.

This invention relates to a new and novel method and apparatus for directing atomized coating material to articles which are to be finished with a protective or decorative coating, and in particular wherein the deposition of the material is accomplished wholly or in part through the medium of an electrostatic field as described in Letters Patent No. 2,334,648, granted November 16, 1943, for "Method of spray coating articles.

In the normal orthodox spray method the coating material, having been atomized by relatively high pressures, travels at quite high velocities only a very short distance from the atomizing or spray gun before encountering the article onto which it is blasted by the direct action of the atomizing air. Only part of the material leaving the gun is applied to the article by this method. The remainder is blown past the article into a collecting water curtain or spray booth and is unused material.

The electrostatic spray method on the other hand employs principles which are quite in contrast to those of the high pressure method. Here it is desirable to have the electrostatic field responsible for precipitating the material onto the article, and the number of particles so precipitated is a direct measure of the efiiciency of the process. To accomplish this, the material must first find itself in the field which exists between the discharge electrode and the item. Introducing the material into this field and retaining it therein sufiiciently long for the relatively weak forces of the field to bring about the precipitation has been one of the chief problems of this method. Prior to this invention it has been the practice to position the atomizing agent in such a way that its atomizing air blast constituted the sole source of positioning the particles in the electrostatic field. However, the directional effects of such a spray are extremely difiicult to control and it is impossible by this practice to have the atomized material remain in the field as finely divided, slowly moving particles sufilciently long for the forces of the field to act upon them and effect eflicient deposition. Due to turbulence, lack of direction and misdirection, a large portion of the material after leaving its spray gun strays from the field, and hence is lost from the action of the field.

It is, therefore, the purpose of the present invention to disclose a method and apparatus by which the dispersed coating particles may be more eifectively and consistently controlled for and prior to their electrostatic deposition.

By the introduction of a gas stream which is completely independent of the atomizing and dispersing agent, the gas stream is caused to absorb the energy the particles acquire during atomization and dispersion and to correct their momentum so that they will travel and remain suspended in the precipitating field for a sufiiciently long time for their deposition to be effected, even though this energy and momentum might alone have been sufiicient to carry the particles into the field.

Also, by suitable direction and control of this auxiliary gas stream with respect to the atomizing agent, the initial velocities which the particles inherently acquire from the atomizing action may be effectually integrated to bring them into a condition of velocity equilibrium with the gas stream in the electrostatic field,

Furthermore, wherein the articles to be coated are continuously passed through the coating zone, such auxiliary gas stream causes the coating material in suspension to be carried along, and preferably counter to, the path of travel of the articles and in a direction perpendicular to that of the lines of force generated in the electrostatic field.

The manner in which these and other objects and advantages of the invention are realized will be described in connection with the accompanying drawings.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims:

Fig. 1 is a perspective view of one form of apparatus with parts broken away and removed.

Fig. 2 is a schematic plan of the invention shown in Fig. 1.

Fig. 3 is a, schematic plan showing a modification of the invention.

For purposes of illustrating the method of and apparatus for coating articles in accordance with this invention, there is shown one form of apparatus having a spray booth comprising an elongated compartment ID for housing and confining the coating zone or space through which the electrostatic coating action takes place. Supported from the ceiling of the spray booth there is a discharge electrode carried by the insulated supports II from which the electrode frame l2 depends, which frame supports a series of equally spaced fine electrode wires l3 connected through the lead-in conductor M with one terminal of a source of high voltage IS. The discharge electrode may comprise a pair of frames l2 spaced from each other and having their electrode wires connected by a connecting lead IS. The opposed electrode frames are so spaced as to permit the articles to be coated to pass between and in a path spaced dErom each of them somewhat greater than the distance of the relative spacing of the electrode wires IS.

The articles I! to be coated are supported in a column and in spaced relation to each other by an overhead conveyor track l8 through the medium of the hanger rods l0. They are moved along a path extending substantially centrally of the spray booth and discharge electrode by a conveyor chain 20. The conveyor system is grounded and through ground is connected with the other terminal of the high voltage source l5. Thus, the articles which are electrically connected through their hangers to the conveyor system are similarly grounded so as to comprise a collecting electrode of the circuit, said electrode being maintained in spaced relation to the discharge electrode wires l3. Between these electrodes there is created a high potential electrostatic field of a character to efiect the electrostatic deposition on the surface of the articles of any coating material spray particles, such as paint, carried into or through this field. Such articles as are shown herein are preferably rotated during their passage through the coating zone to present their entire cylindrical surface to the discharge electrode. Said rotation is caused by engagement of the friction rollers 2| with a rotator bar 22.

The coating material, such as paint or lacquer, is introduced into the electrostatic field, preferably in the form of finely divided particles emanating from the atomizing spray guns 23. One'or' more spray gunsare mounted upon a support 24 and connected through the usual flexible hose with a source of compressed air to provide atomization, as well as with the source of material, in the usual manner. They are adjusted to discharge their spray into the field and substantially toward the articles to be coated.

The articles are caused to continuously travel through the coating zone along a path longitudinally thereof in a direction usually toward the spray guns so that the heavier particles of coating material having the greatest momentum are carried for either impact or electrostatic deposition upon the rearmost articles as they pass into said zone, the finer particles of less momentum being similarly deposited to further coat the articles as they approach the spray guns. However, there will be some loss of material wherein the particles lose their momentum and drop below the coating zone or float away and escape through turbulence or otherwise into a region outside of the effective action of the field and beyond the coating zone, such as the space indicated at 25 between the discharge electrodes and the walls of the booth.

To control and render effective a greater proportion of the coating particles,'a carrier gas current is directed through the field along the path of movement of the articles therethrough. For that purpose the carrier gas may be drawn therethrough by a blower 2G electrically driven by a suitable power source, not shown, said blower being positioned at the end of the spray booth remote from the guns. 4

At that end of the booth towards which the articles progress in their movement and adjacent the spray guns, there are provided inwardly curved ducts 21, 28 extending in close proximity to the path of travel of the articles, and so arranged as to direct the incoming gas, drawn \through the cabinet by the blower, toward said articles and the electrostatic field, so that the greater portion of the current of gas will be concentrated in a stream passing therethrough 1ongitudinally thereof and along the path of travel of the articles. For the purpose of this arrangement, the articles are conveyed into the booth from one side thereof through a restricted tunnel 29 to minimize the amount oi gas bypassed therethrough by the blower.

The gas current so developed assists and augments the atomlzing agent in that it acts as a carrier for the fine particles of the material which have been atomized somewhat in the form of a mist. Additionally, the current of this gas stream smooths out any turbulence and billowing of the spray to prevent particles from being thrown outside of the effective field or coating zone. This gas current also permits of the use of low pressure spray guns which is desirable in electrostatic deposition, by reason of its picking up and carrying the particles along with it lengthwise of the field and in line of travel of the articles. The smaller mist-like particles of the material will, therefore. be caused to slowly move along the path of travel of the articles and continue in that path until they are in position to be conveyed by electrostatic action for deposition, whether at the near or distant position of the articles with respect to the spray guns. For additional control or the path of the carrying gas current, a series of air distributing grills or baflles 30 are arranged between the blower duct 3! and the adjacent end of the spray cabinet.

The aggregate eflect of the forces resulting from the spray ms and the carrying gas stream is such as to insure the slow floating oi the particles along the path of travel of the articles without turbulence and in a direction perpendicular to the direction of the lines of force created by the field. This has the effect of minimizing the otherwise misdirection of many of the coating particles, such as to find themselves outside of the effective field, and causes said particles to be regimented into position for the efficient electrostatic deposition thereof. It is particularly important since the electrostatic forces are perpendicular to the movement of the particles of material introduced into the field, that the particles remain in the field, for a substantial time so that the action of the electrostatic forces will eventually cause their precipitation onto the articles. This is materially assisted and controlled by the auxiliary carrier stream acting to regiment and control the motion of the particles over this required longer period of time, confining them to the field and in efi'ective relation to the oncoming articles.

In Fig. 3 there is shown a modification of the above, wherein the articles 1 are of a peculiar form. requiring a somewhat difierent treatment than as above described. wherein the article to be coated has certain electrically shielded portions into which the electrical field alone will not "throw" sufllcient coating material, it is desirable to utilize the impact force of the spray guns to so direct the spray of coating material as to reach such shielded portions. This applies to items which have deep grooves or slots, or perhaps other formations which may have a shielding eflect, or which may otherwise prevent proper and even electrostatic deposition. In such cases, it is desirable to utilize, at least in part, the blast from the spray guns to cause direct mechanical impact of the particles of coating material on such portion.

Wherein this is desirable, a large portion of the atomized material will blow" past the article, and it is the purpose and function of developing the carrier gas stream above described to pick up and redirect this material to carry it along through the field into position for electrostatic deposition. This arrangement prevents substantial loss of material under such conditions. Usually when it is necessary to direct the material at high velocity toward the article for the mechanical coating of shielded or difiicult portions thereof, the spray guns I23 are directed substantially at right angles to the path of travel of the article. To pick up and recover those particles which blow past the article, the carrier gas stream is arranged in direct opposition thereto. Thus, as in Fig. 3, the baflies I21, I28 are arranged to direct the carrier gas stream first in direct opposition to the spray and thence along the path of travel of the articles through the electrostatic field. The impact of the gas stream will carry the normally lost particles of the material back toward the articles and will retain them in suspension as they are thereby carried into and through the electrostatic field for electrostatic deposition.

The above permits articles of complicated contour to be coated automatically and electrostatically with substantially greater efiiciency and uniformity than has heretofore been possible. Furthermore, by overcoming certain undesirable characteristics of automatic and electrostatic spray operations, as above described, this invention effects considerable savings in coating material, such as paint, and the operation will be conducted with less undesirable paint or coating residue. Also, due to the effect of the carrier stream in promoting an even distribution of coating material along an extended zone of deposition, a gradual building up of the coating film occurs as the article progresses from the furthermost position toward the spray guns through the stream of carrier gas, and the thickness of film obtainable in one operation may be considerably increased with better coating coverage and protection. Thus, items which would normally heretofore be classed as unsuitable for automatic electrostatic spray operation, may now be emciently coated because of the added flexibility resulting from this invention.

The invention claimed is:

1. Apparatus for coating articles including means for conveying an article to be coated along a predetermined path through a spray zone, a discharge electrode mounted in said zone in spaced relation to the article and extending along its path of travel, a source of high voltage electrically associated with said article and electrode to provide a field of high potential difference therebetween, means for atomizing and directing finely divided particles of liquid coating material towards the path of article-travel for electrostatic deposition on the article, means for creating a carrier gas stream, and baflles arranged to direct the gas stream into said field, along the path of travel of said article, and generally perpendicular to the lines of force of said field for picking up and carrying suspended particles of coating material into position to be electrostatically deposited on said article as it passes through said. zone.

2. Apparatus for coating articles including means for conveying an article to be coated along a predetermined path through a spray zone, a discharge electrode mounted in said zone extending along the path of travel of said article, a source of high voltage electrically associated with said article and electrode to provide a. field of high potential difierence therebetween, means for atomizing and directing finely divided particles of liquid coating material toward said path, andmeans for inducing an independent carrier gas stream through said field for receiving suspended particles of coating material and conveying them along the path of travel of said article during its passage through said zone.

3. Apparatus for coating articles including a cabinet, means for conveying a column of articles to be coated through a side wall of said cabinet and thence centrally and longitudinally thereof, a discharge electrode mounted in said cabinet in spaced relation to and extending along the path of travel of said articles, a source of high voltage electrically associated with said articles and electrode to provide a field of high potential difference therebetween, means for atomizing and directing finely divided particles of liquid coating material towards said articles for electrostatic deposition thereon, means for inducing a carrier gas stream along and counter to the path of travel of said articles through said field, and baiile means adjacent the end of said cabinet from which the articles emerge for directing said gas stream toward said articles and into said field.

4. Apparatus for coating articles including an elongated spray cabinet having an outlet end for said articles and a restricted intake passage in the side wall thereof, means for conveying a column of said articles to be coated in spaced relation through said intake passage, longitudinally of said cabinet and through said outlet end, a discharge electrode mounted in said cabinet in spaced relation thereto and extending along the path of travel of said articles, a source of high voltage electrically associated with said articles and electrode to provide a field of high potential difierence therebetween, means for atomizing and directing finely divided particles of liquid coating material towards said column of articles as they pass longitudinally of said cabinet for electrostatic deposition thereon, baiiies provided at the outlet end of said cabinet adjacent said atomizing means extending towards said articles and said field, and a means at the opposite end of said cabinet beyond the path of travel of said articles for drawing a carrier gas through said field and along their path of travel, said baiiies being so arranged as to direct the incoming carrier gas towards said articles and field in the zone of the atomized coating material,

5. Apparatus for coating articles including means for supporting an article to be coated in a predetermined position in a coating zone, a discharge electrode mounted in said zone in spaced relation to said article, a source of high voltage electrically associated with said article or its support and said discharge electrode to provide a field of high potential difierence therebetween, means for atomizing and directing finely divided particles of coating material for electrostatic deposition onto said article, and means for providing a carrier gas stream in addition to the atomizing means for controlling particles of coating material prior to electrostatic deposition onto said article.

6. Apparatus for coating an article, comprising a chamber having near its opposite ends inlet and discharge openings of smaller cross-sectional area than the chamber, means for supporting an article to be coated between said inlet and discharge openings, an electrode spaced laterally of said chamber and from an article supported by said supporting means, a high-voltage source having its opposite terminals associated respectively with said article and electrode to create an electrostatic field therebetween, means for withdrawing air from said discharge opening to create an air stream flowing through 'said field and over the article, and means for introducing finely divided coated material into said air stream prior to its moving into said field.

7. A method of electrostatically depositing a liquid coating material on the surface of an article, comprising creating an air stream of relatively low velocity and confining it laterally to cause it to flow through a zone of deposition in which coating material is to be applied to the article, moving the article over a predetermined path which includes a stretch extending in the zone of deposition longitudinally of said air stream, maintaining an electrostatic field over the surface of the article during its passage through the zone of deposition, and introducing into said stream a relatively high-velocity, divergent jet of atomized liquid coating material, said jet being introduced into said air stream at a point therein upstream from the zone of deposition and being directed generally toward said zone whereby said air stream will supplement the initial momentum of the atomized coating material in causing such material to move into and along the zone of deposition, will insure that undeposited coating-material particles in the zone of deposition possess a minimum velocity longitudinally of said zone, and will materially reduce the relative magnitude of differences between the respective longitudinal velocities of undeposited coating-material particles.

8. A process as set forth in claim 7 with the addition that the path of article-movement includes a second stretch extending laterally of the air stream to a point beyond the limits thereof.

9. A process as set forth in claim 7 with the addition that said air stream is created by withdrawing air from a point beyond one end of the zone of deposition and causing air replacing that withdrawn to enter the zone of deposition from the opposite end thereof.

HAROLD P. RANSBURG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,484,867 Bradley Feb. 26, 1924 1,855,869 Pugh Apr. 26, 1932 2,053,781 Reichel Sept. 8, 1938 2,097,233 Meston Oct. 26, 1937 2,247,963 Ransburg et al July 1, 1941 2,302,289 Brarnston-Cook Nov. 17, 1942 

